In prior art processes, nickel and cobalt bearing ores and concentrates may, for example, be processed by the reduction roast ammonium carbonate oxidative leach route. By this route, impure cobalt sulphide is produced as a by-product, and the isolation and recovery of this by-product is illustrated in Australian Patent 605867.
The recovery of cobalt as a sulphide is achieved by injection of a suitable sulphiding agent, for example, gaseous hydrogen sulphide or ammonium hydrosulphide solution. This procedure however results in the precipitation of sulphides of other elements present such as iron, zinc, copper and nickel as well as the adsorption and or coprecipitation of compounds that normally do not produce insoluble sulphides, such as calcium, magnesium and manganese.
In order to produce pure cobalt metal or a pure cobalt compound for industrial applications it, is necessary to first solubilize the impure sulphides and then isolate the cobalt in a suitable form free of unwanted impurities.
A number of processes have been reported describing the isolation of cobalt as a pure product. These procedures usually involve a combination of solubilization, precipitation, solvent extraction and electrowinning operations. One such process, known as the Nippon Mining Corporation process, recovers cobalt in the metallic form by electrowinning from an acidic sulphate solution. Another process, known as the Sumitomo process, also recovers cobalt in metallic form. However, this is electrowon from a chloride solution. Both of these operations have common features in that the cobalt is present in the cobaltous state at the point of isolation and the produce is a massive metal cathode plate.
Another commercial cobalt sulphide refining process is the soluble cobaltic ammine process developed by Sherritt Gordon Mines Ltd. This process involves solubilization, precipitation of hydrated ferric oxide, conversion of the cobaltous sulphate to cabaltic pentaammine sulphate, precipitation of nickel ammonium sulphate, reduction of the cobaltic pentaammine to cobaltous diammine and, finally, pressure hydrogen reduction to cobalt metal powder.
Cobalt has many applications and not all of these require cobalt metal. For example, cobalt salts find use in a variety of industries and significant quantities of cobalt oxide is also used industrially. Consequently, a pure cobalt compound able to be converted to salts, oxides and fine metal powder would be a useful industrial commodity.
The present invention aims to overcome, or at least alleviate, one or more of the difficulties associated with the prior art.